GMAW welding is a common industrial weld process because of its versatility, weld travel speed, and the relative ease of adapting the process to robotic automation. In single wire GMAW processes, a single continuous and consumable electrode wire and a shielding gas are fed through a welding torch.
To obtain higher welding speed, a double wire GMAW welding apparatus and process has also been developed, which employs two electrically isolated wire electrodes for combining two welding arcs in one weld pool. In such a double wire GMAW process, a welding torch is provided with two wire electrodes. Compared with the conventional single wire welding processes, the double wire GMAW process can obtain a substantial increase in welding speed. Therefore, the double wire GMAW process has been increasingly employed in industrial welding applications that require high productivity, performance, and deposit rate, such as tank construction, boiler engineering, vehicle manufacturing, automotive and railway constructions and shipbuilding, etc. Such a double wire GMAW welding is known from U.S. Pat. Nos. 5,155,330, 6,683,279, US Patent Publication Nos. 2006/0243704, 2007/0145028, and EP Patent No. 1294522.
The GMAW weld quality depends on many factors, conditions, and considerations, such as wire feeding, shielding gases, base materials and thickness of work pieces to be welded and metal transfer modes. Also, the dynamics of welding parameters are complex, and the establishment of a stable arc depends on a series of conditions involving welding current, power supply voltage, wire feed speed, torch traveling speed, distance between a contact tip and a work piece (hereinafter referred to as tip-to-work distance), and torch angle, in order to achieve a desired weld. The situation becomes more complex when two electrode wires are utilized in the double wire GMAW welding apparatus and process.
In use, because electric arc sizes vary in length and width with changes in the above parameters for variable welding requirements, these two electric arcs might get close to a point of interfering with each other as a result of the electromagnetic arc blow effect, which dramatically affects the process stability and spatter degree. This can make the process technically infeasible. It is therefore desirable to adjust the wire spacing with regard to a particular weld condition, in order to minimize the wire interference.
A synchronized pulsed welding method has recently been developed, which uses a pulsing current to melt the electrode wire and allow one small molten droplet to fall with each pulse. The pulse provides a stable arc and no spatter, since no short-circuit takes place. However, the necessity of utilizing complex arc pulsing conditions may limit the broad application of the double wire synchronized pulsed welding process, due to the extra requirement on the power sources capabilities. For example, it requires a special power source capable of providing current pulses with a frequency within a certain range, such as 30-400 pulses per second. Moreover, a controller is needed to synchronize the two arcs. As a result, there exists a need for a non-synchronized double wire welding process with the same capabilities as the synchronized pulsed-spray welding, such as the stable weld process, but without spatter.
U.S. Pat. No. 5,155,330 discloses a double wire GMAW welding method and apparatus. The method involves two welding electrodes to be connected to a single power source for a welding process. The apparatus comprises an interchangeable elongated, electrically conductive welding wire guide member having a cylindrical body including a first and second wire, which are spaced from each other with the centerline distance between 4.7-9.4 mm by changing the angles of the contact tips.
US Patent Publication No. 2006/0243704 discloses a method and apparatus of welding using at least two consumable electrodes. When two wire electrodes are used, the first one is larger in diameter compared to the second and a common weld pool is produced. A changeable distance between 3-12 mm is disclosed, and this distance range is obtained by means of changing the tip-to-work distance of the two non-parallel electrodes. It is disadvantageous during the welding process in that the tip-to-work distance is an important variable, and that the tip-to-work distance is usually required to be kept within an optimal range for an eligible weld.
Although the above-mentioned double wire GMAW welding processes have been developed, there remains room for further improvement in the art.